1. Field of the Invention
The present invention relates to a magnetic repulsion-actuated magnetic bearing and, more particularly, to a non-contact type magnetic bearing for use in a rotary mechanism such as a motor, power generator, flywheel mechanism, vacuum pump, chemical pump, or the like.
2. Description of Related Art
Following fast development of semiconductor and liquid crystal display manufacturing apparatus and equipments, high speed rotary mechanisms are desired. In recent years, non-contact type bearings are intensively used in rotary mechanisms for the advantages of low friction, low noise, and low vibration. Following the progress of digital control and power electronic technology, magnetic bearings have become the majority choice among non-contact type bearings. Conventional magnetic bearings include magnetic attraction-actuated magnetic bearings and magnetic repulsion-actuated magnetic bearings. Magnetic repulsion-actuated magnetic bearings are commonly of a passive permanent magnet type. This design is seen in U.S. Pat. Nos. 5,152,679; 5,545,937. There are also magnetic repulsion actuators formed of permanent magnets and electromagnets. This design is seen in U.S. Pat. No. 6,147,422.
However, the conventional magnetic attraction-actuated magnetic bearings or magnetic repulsion-actuated magnetic bearings are still not satisfactory in function. According to conventional designs, a magnetic attraction-actuated magnetic bearing requires a bias current as a reference of control. When without load or external interference, a magnetic attraction-actuated magnetic bearing still consumes much electric energy, and its inherent high inductance resulted from the low leakage magnetic linkage/loop inhibits increasing of rotation speed. The inductance of the magnetic loop of a magnetic repulsion-actuated magnetic bearing is low, however its flux lines dissipate severely, not able to effectively inhibit interference and maintain stiffness.
Therefore, it is desirable to have a magnetic bearing that eliminates the aforesaid problems.
It is the main object of the present invention to provide a magnetic repulsion-actuated magnetic bearing, which retains radial bearing stiffness upon power failed.
It is another object of the present invention to provide a magnetic repulsion-actuated magnetic bearing, which utilizes a by-pass magnetic loop structure to shape the flux lines distribution, so as to improve the stiffness of the magnetic bearing.
It is still another object of the present invention to provide a magnetic repulsion-actuated magnetic bearing, which provides axial bearing by means of axial offset of magnets.
It is still another object of the present invention to provide a magnetic repulsion-actuated magnetic bearing, which enhances the magnetic force of repulsion by arranging a permanent magnet at the front end of the iron core.
To achieve these and other objects of the present invention, the magnetic repulsion-actuated magnetic bearing is comprised of a stator, at least two magnetic repulsion modules, a rotor, and a controller. The stator has an inside wall defining an axially extended receiving hollow chamber. The magnetic repulsion modules each comprise a plurality of magnetic repulsion actuators equiangularly arranged on the inside wall of the stator. Each magnetic repulsion actuator comprises an iron core having a first end fixedly fastened to the inside wall of the stator and a second end radially extended to the receiving hollow chamber, a permanent magnet located on the second end of the iron core, and a winding wound around the iron core and adapted to produce a magnetic force when electrically connected. The rotor is axially received in the receiving hollow chamber of the stator, comprising at least two annular permanent magnets arranged around the periphery thereof corresponding respectively to the at least two magnetic repulsion modules, each annular permanent magnet defining with the permanent magnet of the magnetic repulsion actuator of the corresponding magnetic repulsion module a working air gap. The polarity of each annular permanent magnet is same as the polarity of the permanent magnet of the magnetic repulsion actuator of the corresponding magnetic repulsion module so that a radial magnetic force of repulsion is produced between each annular permanent magnet of the rotor and the permanent magnet of the magnetic repulsion actuator of the corresponding magnetic repulsion module. The controller is electrically connected to the windings of the at least two magnetic repulsion modules, and adapted to respectively control the current of the windings to change the intensity of magnetic force of the at least two magnetic repulsion modules so as to change the net radial magnetic force of repulsion between the annular permanent magnet of the rotor and the permanent magnet of the magnetic repulsion actuator of the corresponding magnetic repulsion module respectively.
Therefore, when power failed, a radial magnetic force of repulsion is produced between the permanent magnets of the stator and the corresponding annular permanent magnets of the rotor. Because the permanent magnets are arranged at the front ends of the respective iron cores corresponding to one end of the rotor, the force of repulsion between the permanent magnets and the annular permanent magnets is enhanced to keep the rotor in balance automatically when power failed. Therefore, the rotor is maintained floating stably when electric current turned off. On the contrary, when electric current turned on, the controller controls the windings of the equiangularly spaced magnetic repulsion actuators to increase or reduce the magnetic force of the corresponding iron cores respectively, so as to change the radial magnetic force of repulsion of the respective magnetic repulsion actuators. Therefore, when the rotor radially biased toward one side, the controller increases the radial magnetic force of repulsion of the magnetic repulsion actuators at the corresponding side and reduces the radial magnetic force of repulsion of the magnetic repulsion actuators at the opposite side, the position of the rotor is maintained stable, and therefore, the rotor is maintained in stiffness in radial direction during rotation.
Further, each magnetic repulsion module further comprises a pair of annular magnetic poles located at two sides axially. The pair of annular magnetic poles each have the respective outside wall fixedly fastened to the inside wall of the stator, and at least one magnetic pole protrusion inwardly protruded from an inside wall of the annular magnetic pole and aimed at the respective permanent magnet of the corresponding magnetic repulsion actuator. The opposite magnetic pole protrusions of the pair of annular magnetic poles define an opening therebetween for receiving the respective permanent magnet of the corresponding magnetic repulsion actuator without contact. Therefore, a by-pass loop is formed between the annular magnetic poles and the permanent magnets to cause a change of the flux lines distribution around the actuators fringe from free diversion, forming an integral loop, and hence provides higher current efficiency and bearing stiffness. The present invention also could use a pair of annular magnetic paths arranged around the periphery of the rotor and spaced from the corresponding annular permanent magnet of the rotor at two sides axially by a gap to form a by-pass loop to achieve the object aforementioned.
The magnetic repulsion-actuated magnetic bearing can be designed having two annular permanent magnets and two magnetic repulsion modules. The two annular permanent magnets are axially spaced around the inside wall of the stator at two ends and respectively aimed at the permanent magnets. The annular permanent magnets are reversed in polarity. The two magnetic repulsion modules and the two annular permanent magnets are arranged in an axial offset manner. The axial distance between the two annular permanent magnets is slightly greater than the axial distance between the two magnetic repulsion modules. The axial offset arrangement of the two magnetic repulsion modules and the two annular permanent magnets achieves balancing in axial direction, i.e., a magnetic force of repulsion is produced at one side to push the rotor in one direction, and a magnetic force of repulsion is produced at the other side to push the rotor in the reversed direction, keeping the rotor in stiffness in axial direction. Same effect can be achieved when the axial distance between the two annular permanent magnets set shorter than the axial distance between the two magnetic repulsion modules.